The present invention is in general related to manipulation of a stage and, more particularly, to manipulation of a fully released stage in a decoupled manner according to closed-loop feedback with sub-micron accuracy.
Scanning probe microscopes (SPMs) are devices which manipulate a scanning probe with sub-atomic accuracy to scan the surface of a sample object or material. For example, the scanning tunneling microscope (STM) is a solid-state microscope based on the principle of quantum mechanical tunneling of electrons between a sharp tip and a conducting sample. The tip of an STM is an extremely sharp metal tip. The tip is mounted on a system of piezoelectric drives which are controllable with sub-atomic precision. The scanning process begins by bringing the tip within a few Angstroms of the conducting sample surface. At such separations, the outer electron orbitals of the tip and the sample overlap. Accordingly, on the application of a bias voltage between the tip and the surface, electrons tunnel through the vacuum barrier via the quantum mechanical tunneling effect, even though the tip and the surface are not in physical contact. By scanning the tip across the sample surface, it is possible to image directly the three-dimensional real space structure of a surface at atomic resolutions.
To provide the necessary scanning resolution, scanning operations of an SPM are typically implemented utilizing a piezo element. FIG. 1A depicts a block diagram of a typical SPM 100 according to the prior art. The sample 103 to be scanned is placed on stage 102. Control means 105 causes a suitable voltage to be applied to piezo element 104. In response to the applied voltage, piezo element 104 controllably expands. Utilizing suitably designed piezo element 104, the expansion may occur in any of the X-direction, Y-direction, and Z-direction. In typical operations, control means 105 controls the vertical distance (in the Z-direction) between scanning tip 101 and sample 103. Also, control means 105 causes piezo element 104 to move scanning tip 101 over sample 103 according to, for example, a raster pattern in the X and Y-directions. The control of piezo element 104 may utilize various feedback techniques such as examining the tunneling current associated with scanning tip 101. Also, other feedback techniques may be utilized such as optical feedback, capacitive feedback, and piezo-resistive feedback (not shown). The imaging signal associated with scanning tip 101 may be provided to imaging system 106 for suitable processing. When piezo element 104 is utilized, the dimensions of SPM 100 are typically on the order of ten centimeters. Accordingly, the scanable area of an object placed on stage 102 is quite small relative to the size of SPM 100.
Moreover, XY stages that are controllable on precise resolutions are used for a variety of applications. For example, XY stages may be utilized to control a micro-lens for optical applications. FIG. 1B depicts XY stage 150 according to the prior art which is operable to control lens 155. XY stage 150 comprises a plurality of cascaded thermal actuators (151-154). The thermal actuators (151-154) are mechanically coupled to lens 155 via respective general purpose flexures which are generally known for use to facilitate actuation in Micro-Electrical-Mechanical (MEMs) devices. Actuators 152 and 154 enable displacement of lens 155 in the Y-direction and actuators 151 and 153 enable displacement of lens 155 in the X-direction. However, the design of XY stage 150 does not fully decouple the manipulation of lens 155 in the X and Y directions. Specifically, displacement of lens 155 in the X-direction by actuators 151 and 153 will also cause some amount of displacement in the Y-direction. Likewise, displacement of lens 155 in the Y-direction by actuators 152 and 154 will also cause some amount of displacement in the X-direction.
Thus, known structures that manipulate high resolution XYZ stages either (1) are associated with coupled movement where actuation in one direction causes a lesser degree of actuation in another direction; (2) require bulky piezo elements to achieve the desired non-coupled movement; or (3) are permanently anchored to the substrate on which they were fabricated.
Additionally, it is appropriate to note that various techniques exist for post-fabrication assembly of MEMs devices. For example, xe2x80x9cflip-chipxe2x80x9d bonding is well-known in the art for bonding two discrete structures after fabrication of the structures. However, flip-chip bonding is problematic, because it imposes a relatively simple mechanical design via the bonding of a first flat surface to a second flat surface. Thus, flip-chip bonding prevents assembly of structures with surface features and, hence, reduces the potential complexity of devices assembled utilizing this technique.
The present invention is directed to a system and method which are operable to manipulate a fully released stage to provide decoupled movement that is controlled by suitable closed-loop feedback. In embodiments of the present invention, the XY positioning of the stage may be advantageously manipulated using a first plurality of actuators (e.g., comb drives, parallel plate actuators, shaped memory alloy (SMA) actuators, electrothermal actuators, piezo stack actuators, and/or the like) and a second plurality of actuators. In embodiments of the present invention, the actuators are implemented as flexure amplified banks of bent beams that each occupy approximately 400 microns in length. By utilizing actuators of this scale, the total size of the device may be significantly reduced. In embodiments of the present invention, the entire device may be approximately one millimeter in length.
Moreover, the actuators may be advantageously coupled to flexures which are, in turn, coupled to the stage. The actuators and the flexures are positioned and operate in a mirrored manner. Specifically, when it is desired to actuate the stage in the X-direction, two corresponding mirrored actuators are supplied current. The actuators move the stage in the desired direction via the coupled flexures. It shall be appreciated that the same actuators that cause the actuation in the X-direction may also produce undesired forces in the Y-direction. If the undesired forces are not addressed by embodiments of the present invention, the forces will produce coupled movement. However, embodiments of the present invention utilize the mirrored positioning and flexures to balance the undesired forces in the Y-direction. Thus, the total torque on the stage is approximately zero. Actuation in the Y-direction may also utilize a mirror positioning and operation of movements to decouple movement in the Y-direction. Thus, actuation in the X-direction and the Y-direction are fully decoupled. A third actuator may also be utilized to actuate the stage in the Z-direction. Also, suitable feedback structures (capacitive, optical, piezo-resistive, and/or the like) may be utilized to control the manipulation of the stage.
The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims. The novel features which are believed to be characteristic of the invention, both as to its organization and method of operation, together with further objects and advantages will be better understood from the following description when considered in connection with the accompanying figures. It is to be expressly understood, however, that each of the figures is provided for the purpose of illustration and description only and is not intended as a definition of the limits of the present invention.